Field of the Invention
The invention relates to an instrument consisting of a container for collection of undisturbed soil samples, a method of collecting, preparing and analysing undisturbed soil samples, and an equipment for defining soil hydraulic conductivity in laboratory conditions.
Brief Description of the Background of the Invention Including Prior Art
Infiltration properties of soil are a very important question for several areas of science and industry, for instance geology or hydrology. Therefore in laboratory research on water permeability of key significance is collection of material to be analysed, its preparation and performing the analysis in such conditions and using such equipment that will guarantee reliable and repeatable results.
Especially in anisotropic soils, presence of dry particles and root systems directly influences filtration properties of such soil. In case of forest soils, there is another factor determining the value of hydraulic conductivity, namely high content of organic matter in various stages of decay, coming from organic matter falling down and dead roots. These elements have a significant impact on results, as water infiltrating downward goes around such obstacles (soil skeleton and root systems). For the results to be reliable and reflecting reality, the collected soil sample must retain its natural structure, i.e. be physically as similar to natural conditions as possible, otherwise the measurements will be prone to a huge error (reaching up to several hundred percent).
Numerous methods of analysis of hydraulic conductivity, both on-site and in laboratory conditions, have been described in literature, suggesting existence of several methods and devices used for the purpose of such research. In commonly used methods, collecting undisturbed soil samples is only possible in case of uniform soils, i.e. sand, clay/silt, dust. If, however, the sample is to contain the so-called skeleton and root system, the problem starts. It is even more problematic if the soil to be analysed comes from slopes of various gradients and samples should reflect natural water flow (consistent with the direction of gravitational infiltration).
The generally applied method of soil sampling is the removal of soil with a cutting ring. Frequently, a sample obtained in this way is tested without further processing. Sometimes, if the structure of the sample was compromised during sampling, it is homogenised. The prepared sample is placed in a pressure column, and later saturated with water. Then a pressure similar to the one that would be exerted on the sample in natural conditions is produced in the column. The defining of hydraulic conductivity is based on the linear Darcy's Law and means the measurement of the volume of water flowing through the sample and escaping through designated openings in a specified time, with specified hydraulic drop and temperature. In methods known in state of the art, the flow of the water is usually not aligned with the natural direction of filtration which generates further distortions in the results achieved.
Known from the Polish patent application no. P.389144 is a device for simultaneous sampling of monolith and samples of soft deposits. The device is equipped with the upper and lower cones, whose bases are permanently connected with the semi-cylindrical wall of the tube. In turn, the bases are connected with axles, in a semi-turn manner, to the thrust runner, whose one part is set in a semi-cylindrical wall. Mounted to it is a vertical column of the measurement cylinders for deposit samples cut out with the cylindrical blade situated below, while the device is being plunged. At the desired depth, the horizontal rotation of the pole cuts out a semi-cylindrical monolith of the analysed structure with its vertical edge and encloses it together with the samples in the device.
Known from the Polish patent application no. P.389934 is a set for sampling soil profiles. The set consists of a cylinder with an extruder, with arms and connector set on the edges, and a lever which is connected to the mast by means of hinges. Mounted on the mast is a grip, which is fixed in the sockets of the frame in a way enabling disconnection. While pressing the soil profile, the cylinder is placed in the stabiliser.
Known from general use is the ZW-K2 device produced in Poland, which consists from a double steel vessel with water inlets and outlets, a system for lateral deaeration, millimeter scales, perforated base of the internal vessel with mesh size of 0.2 mm, a ring (form) of 113 mm in diameter and 60 mm in height, the top cap with a mesh of 0.2 mm and a weight. This device is equipped with a bottom deaeration system which consists of a number of ducts situated under the sample, which frequently become disconnected while assembling the container with a sample. It is equipped with containers with a flange securing them in the device with the use of screws. Damage of the screws securing the container with the sample results in the destruction of the entire device. The height of the containers is set and amounts to 6 cm, which renders testing of soil strata with thickness below 6 cm impossible. The device allows achieving the maximum hydraulic drop of 2.0, which does not allow testing water permeability of poorly permeable soils.
Soil samples obtained with such devices have strongly compromised structure. The root systems and soil skeleton contained in the sample are shifted. Lack of proper preparation of the sample and also testing it in conditions that are clearly different from the natural conditions result in results fraught with errors difficult even to estimate.
Most of the factors influencing the origination of irregularities in the process of sampling, preparation, and measurements conducted was eliminated thanks to the development of the solutions below.